The present invention pertains to processes for printing substrates and substrates printed thereby, and more specifically to processes for printing elongate, semi-tone graphics on substrates, and substrates printed thereby.
The printing of substrates, such as woven and nonwoven fabrics and films, is well known. The printing of fabrics with inks and dyes is a common and widely used method for imparting patterns and colors to a basic fabric. Many current personal care products, such as diapers and training pants, include printed patterns on portions thereof to improve their appearance. These printed portions are generally non-elastic, which makes the printing of patterns thereon a straightforward and conventional printing exercise. However, significant problems arise when the substrate, or portions thereof, to be printed is elastic, or, after being printed, then will be elasticized.
One problem occurs when a high resolution and high definition printed pattern is desired on an elastic substrate. In this instance, the elastic substrate generally is fully extended to allow ink to be printed on the entire pattern field. This is necessary in order to eliminate unprinted void areas that occur when the elastic substrate is printed in its relaxed, contracted state. These unprinted void areas exist because the unelevated, or trough, portions of the relaxed, contracted elastic substrate do not come in direct and full contact with the printing apparatus. Consequently, the unelevated, or trough, portions are not fully, if at all, printed.
Unfortunately, in many cases the printing of elongated elastic substrates has proven to be cost prohibitive. This is due to having to use carrier sheets in some printing processes to prevent ink from striking through the extended, and thus thinner, elastic substrate. The carrier sheets are an added expense, as is their replacement when worn.
Another problem is the inability to keep a constant tension on an elastic substrate that is continuously moving at high speeds. The high speeds, and the physical handling of the elastic substrate at these high speeds, causes the tension on the elastic substrate to vary, which can produce patterns that are misregistered, blurred, and/or incorrect in their dimensions.
Yet another problem with printing elastic substrates occurs when the elastic substrate is elastic in the cross-direction, i.e., the direction transverse to the direction the substrate is continuously moving. The cause of this problem is an inability to extend or elongate the elastic substrate in the cross-direction during a continuous printing process.
An added problem occurs when the substrate to be printed is a low basis weight material. Because low basis weight substrates inherently include a large number of small voids, or a smaller number of larger voids, any ink or inks printed thereon can run through, i.e., strikethrough, the substrate. The problem with ink strikethrough is that the ink builds up on the printing apparatus. This ink buildup on the printing apparatus results in poor print quality on the substrate, the transfer of ink to the back of the substrate, and poor operating efficiency due to machinery down time required to remove the ink buildup.
This problem becomes even more significant in high speed printing environments, since ink buildup is accelerated, thereby increasing the number of times the machinery needs to be shut down for removal of the buildup. As shutdown times increase, so do waste of material and ink that are associated with machinery startup.